This application claims the benefit of Korean Patent Application Nos. 1999-67855 filed on Dec. 31, 1999 under 35 U.S.C. xc2xa7119, the entirety of which is hereby incorporated by reference,
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD)) device, and more particularly, to a transflective LCD device.
2. Description of Related Art
In general, liquid crystal displays are divided into transmissive LCD devices and reflective LCD devices according to whether the display uses an internal or external light source.
A typical transmissive LCD device includes a liquid crystal panel and a back light device. The liquid crystal panel includes upper and lower substrates with a liquid crystal layer interposed. The upper substrate includes a color filter, and the lower substrate includes thin film transistors (TFTs) as switching elements. An upper polarizer is arranged on the liquid crystal panel, and a lower polarizer is arranged between the liquid crystal panel and the backlight device.
The two polarizers have a transmittance of 45% and, the two substrates have a transmittance of 94%. The TFT array and the pixel electrode have a transmittance of 65%, and the color filter has a transmittance of 27%. Therefore, the typical transmissive LCD device has a transmittance of about 7.4% as seen in FIG. 1, which shows a transmittance (in brightness %) after light passes through each layer of the device. For this reason, the transmissive LCD device requires a high, initial brightness, and thus electric power consumption by the backlight device increases. A relatively heavy battery is needed to supply a sufficient power to the backlight of such a device. However, this has a problem that the battery can not be used for a lengthy period of time.
In order to overcome the problem described above, the reflective LCD has been developed. Since the reflective LCD device uses ambient light, it is light and easy to carry. Also, the reflective LCD device is superior in aperture ratio to the transmissive LCD device.
FIG. 2 shows a typical reflective LCD device in cross section. As shown in FIG. 2, the reflective LCD device includes upper and lower substrates 8 and 10 with a liquid crystal layer 12 interposed. The upper substrate 8 includes color filter layers 4a, 4b and 4c (e.g., red, green, and blue) and a common electrode 6. The lower substrate 10 includes a switching element (not shown) and a reflective electrode 2.
Ambient light 100 passes through the upper substrate 8 and the liquid crystal layer 12 and is reflected on the reflective electrode 2. When electrical signals are applied to the reflective electrode 2 by the switching element, phase of the liquid crystal layer 12 varies. Then, reflected light is colored by the color filter layers 4a, 4b and 4c and displayed in the form of images.
However, the reflective LCD device is affected by its surroundings. For example, the brightness of ambient light in an office differs largely from that outdoors. Even in the same location, the brightness of ambient light depends on the time of day (e.g., noon or dusk).
In order to overcome the problems described above, a transflective LCD device has been developed. FIG. 3 shows a conventional transflective LCD device. As shown in FIG. 3, the conventional transflective LCD device includes upper and lower substrates 22 and 18 with a liquid crystal layer 20 interposed. The upper substrate 22 includes a color filter 104, and the lower substrate 18, referred to as an array substrate, includes a switching element (not shown), a pixel electrode 14 and a reflective electrode 2. The reflective electrode 2 is made of an opaque conductive material having a good reflectance and light transmitting holes xe2x80x9cAxe2x80x9d are formed therein. The transflective LCD device further includes a backlight device 16. The light transmitting holes xe2x80x9cAxe2x80x9d serve to transmit light 112 from the backlight device 16,
The transflective LCD device in FIG. 3 is operable in transmissive and reflective modes. First, in reflective mode, the incident light 110 from the upper substrate 22 is reflected on the reflective electrode 2 and directed toward the upper substrate 22. At this time, when electrical signals are applied to the reflective electrode 2 by the switching element (not shown), phase of the liquid crystal layer 20 varies and thus the reflected light is colored by the color filter 104 and displayed in the form of images.
Further, in transmissive mode, light 112 generated from the backlight device 16 passes trough portions of the pixel electrode 14 corresponding to the transmitting holes xe2x80x9cAxe2x80x9d. When the electrical signals are applied to the pixel electrode 14 by the switching element (not shown), phase of the liquid crystal layer 20 varies. Thus, the light 112 passing through the liquid crystal layer 20 is colored by the color filter 104 and displayed in the form of images.
Detailed explanation of the transflective LCD device and the fabrication method will be provided with reference to FIGS. 4, 5A and 5B. FIG. 4 is a partially enlarged plan view of an array substrate for a transflective LCD device according to a conventions art. As shown in FIG. 4, the array substrate has gate and data lines 25 and 27 crossing each other. A pixel region xe2x80x9cpxe2x80x9d is defined by the crossing. As a pixel electrode 19, there are a transparent electrode 19a and a reflective electrode 19b in the pixel region xe2x80x9cpxe2x80x9d. The reflective electrode 19b has a reflective region xe2x80x9cCxe2x80x9d and a transmitting hole xe2x80x9cAxe2x80x9d as a transmitting region through which light from the backlight is transmitted. The pixel electrode 19 receives a signal from a TFT xe2x80x9cTxe2x80x9d having gate, source and drain electrodes 61, 63 and 65. The gate and source electrodes 61 and 63 are respectively extended from the gate and data lines 25 and 27. The drain electrode 65 is connected to the transparent and reflective electrodes 19a and 19b through first and second drain contact holes 65 and 71.
A fabrication method will be explained with reference to FIGS. 5A and 5B which are cross sectional views taken lines IVxe2x80x94IV and Vxe2x80x94V of FIG. 4, respectively. First, on a substrate 59 a gate line 25 having a gate electrode 61 is formed. On the gate line 61, a first insulating layer 60 is formed using an organic material such as acetyl or benzocyclobutene (BCB) or an inorganic material such as silicon nitride or silicon dioxide. On the first insulating layer 60 over the gate electrode 61 sequentially formed are an active layer 62, source and drain electrodes 63 and 65, and a second insulating layer 64 having the first drain contact hole 67. On the second insulating layer 64 formed is the transparent electrode 19a contacting the drain electrode 65 through the first drain contact hole 67. The transparent electrode 19a has a hole corresponding to the second drain contact hole 71 that will be formed later.
Next, on the transparent electrode 19a an insulating material is deposited and patterned to form the protection layer 69 having the drain contact hole 71 exposing the drain electrode 65. On the protection layer 69 is formed the reflective electrode 19b having the transmitting hole xe2x80x9cAxe2x80x9d at the pixel region. The reflective electrode 19b contacts the drain electrode 65 via the second drain contact hole 71.
Meanwhile, since there are two electrodes 19a and 19b contacting the drain electrode 65 for pixel electrode 19 in this structure, the electric field applied to the liquid crystal can be deflected due to the difference of locations of the two electrodes 19a and 19b, leading to lower the driving efficiency of the liquid crystal. Further, since the second drain contact hole is deep enough to result in a crack of the protection layer 69 or the reflective electrode at the corresponding position, the resistance of the reflective electrode can increase than expected, and particles can be positioned at the crack position.
In order to overcome the problem, it can be considered to form a stacked structure of the transparent and reflective electrodes 19a and 19b, but when forming the transmitting hole xe2x80x9cAxe2x80x9d for the reflective electrode 19b, the transparent electrode can be hurt. Further, the etchant can react with the two electrodes 9a and 9b, lowering the characteristics of the electrodes.
Accordingly, the present invention is directed to a transflective liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the invention is to provide a transflective LCD device that can reduce the deflection of electric field applied to the liquid crystal.
Another object of the invention is to provide a fabrication method of the transflective LCD device that is comprised of simple steps.
In accordance with the purpose of the invention, as embodied and broadly described, in one aspect the invention includes an array substrate for a transflective liquid crystal display device, including: a thin film transistor having gate, data and drain electrodes on a transparent substrate; an insulation layer over the substrate while covering the thin film transistor, the insulating layer having a drain contact hole exposing tie drain electrode of the thin film transistor; a reflective electrode having a transmitting hole on the insulation layer; and a transparent electrode covering the reflective electrode entirely, wherein either of the reflective electrode or the transparent electrode contacts the drain electrode via the drain contact hole of the insulation layer.
The reflective electrode beneficially has aluminum.
In another aspect of the invention, provided is a method of fabricating an array substrate for a transflective LCD device, including: forming a thin film transistor on a substrate, the thin film transistor having a gate electrode, a source electrode, and a drain electrode; forming an insulation layer on the thin film transistor; forming a drain contact hole exposing the drain electrode of the thin film transistor by patterning the insulation layer; forming a reflective electrode having a transmitting hole on the insulation layer; and forming a transparent electrode entirely covering the reflective electrode, wherein either of the reflective electrode or the transparent electrode contacts tile drain electrode via the drain contact hole.
Forming the drain contact hole can be processed, before forming the reflective electrode, thereby the reflective electrode contacting the drain electrode via the drain contact hole.
When forming the drain contact hole is processed after forming the reflective electrode, the transparent electrode contacts the drain electrode via the drain contact hole.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate one embodiment of the invention and together with the description serve to explain the principles of the invention.